1. Field of the Invention
The present invention relates to a lubricant supply device that scrapes a lubricant off a solid lubricant by contacting and rubbing the solid lubricant to supply the lubricant to a lubricant supply target, and a process cartridge and an image forming apparatus such as a copying machine, a printer and a facsimile including the same.
2. Description of the Related Art
As this kind of lubricant supply device, for example, there is known a lubricant supply device described in Japanese Patent Application Laid-open No. 2007-293240. The lubricant supply device described in Japanese Patent Application Laid-open No. 2007-293240 includes a brush roller (supply member) that contacts a solid lubricant having a bar shape and supplies a powdery lubricant scraped by rubbing the solid lubricant, to a photosensitive element belt or an intermediate transfer belt (lubricant supply target). The solid lubricant is pressed against the brush roller by a pressing mechanism. When the brush roller rotates, the solid lubricant that is in contact with the brush roller is rubbed. Thereby, the lubricant, which is scraped off the solid lubricant and is attached to the brush roller, is applied to the surface of the photosensitive element belt or the intermediate transfer belt. In the lubricant supply device, the pressing mechanism presses the solid lubricant against the brush roller in a manner such that the contact pressure between the solid lubricant and the brush roller is constant from the initial stage to the last stage, even though the solid lubricant is gradually scraped off every when the brush roller contacts and rubs the solid lubricant.
FIG. 15 is a partially enlarged view showing a main portion of the pressing mechanism of the lubricant supply device that is described in Japanese Patent Application Laid-open No. 2007-293240. FIG. 15 shows the main portion of the pressing mechanism of the lubricant supply device when viewed from a direction orthogonal to both of a longitudinal direction (horizontal direction in the drawing) of a solid lubricant 162 and a pressing direction (vertical direction in the drawing) of the solid lubricant 162 with respect to a brush roller 161. FIG. 15 is an enlarged view of one end side of the solid lubricant 162 in the longitudinal direction. The configuration of the other end side of the solid lubricant 162 in the longitudinal direction is the same as the configuration of one end side.
A pressing mechanism 463 is provided with a lubricant holding member 162A that holds a portion (on lower side in the drawing) of the solid lubricant 162, in which the portion is opposite to a portion contacting the brush roller 161 in the longitudinal direction. To each of both ends of the lubricant holding member 162A in the longitudinal direction, attached is a movable member 463A that functions as a pressing member, as shown in FIG. 15. One end (attachment end) of the movable member 463A is attached rotatably with respect to the lubricant holding member 162A and the other end (rotating end) rotates in a direction of an arrow C in the drawing using the attachment position 163B as a fulcrum (rotation center). To the movable member 463A, each end of a single spring 163C that is a single biasing unit is attached. Each movable member 463A obtains the biasing force of a direction of an arrow D in the drawing, which is directed to the center of a longitudinal direction of the lubricant holding member 162A from the single spring 163C. By this biasing force, the rotating end of each movable member 463A obtains the rotating force in a direction that gets away from the lubricant holding member 162A, as shown in FIG. 15. Each movable member 463A has a contact portion where a section cut along a surface parallel to both a longitudinal direction of the solid lubricant 162 and a pressing direction of the solid lubricant 162 with respect to the brush roller 161 has a circular arc shape. The contact portion contacts a fixing wall (contacting portion) 164 that is a surface parallel to the longitudinal direction of the solid lubricant 162 and orthogonal to the pressing direction of the solid lubricant 162 with respect to the brush roller 161, by the biasing force of the single spring 163C to rotate each movable member 463A. The contact portion of each movable member 463A contacts the fixing wall 164 and the biasing force of the single spring 163C that rotates each movable member 463A biases the lubricant holding member 162A holding the solid lubricant 162 in a direction apart from the fixing wall 164. As a result, the solid lubricant 162 is pressed against the brush roller 161. The two movable members 463A receive the biasing force of the single spring 163C and press the fixing wall 164 with the equal force. Therefore, the solid lubricant 162 is equally pressed against the brush roller 161, in a longitudinal direction thereof. As a result, the amount of the lubricant that is rubbed and scraped off by rotation of the brush roller 161 becomes uniform in the longitudinal direction, and the lubricant can be coated on a surface of a photosensitive element 5 without unevenness.
The pressing mechanism 463 that is described in Japanese Patent Application Laid-open No. 2007-293240 is advantageous to a general pressing mechanism shown in FIG. 16 in the following points.
In the pressing mechanism 563 shown in FIG. 16, when the height of the solid lubricant 162 decreases over time, the pressing force of the solid lubricant 162 gradually decreases. For this reason, the amount of the solid lubricant 162 that is scraped off by the brush roller 161 temporally decreases, and the change of the amount of powdery lubricant that is supplied to the lubricant supply target from the initial stage to the last stage is large. Meanwhile, in the pressing mechanism 463 that is described in Japanese Patent Application Laid-open No. 2007-293240, even though the height of the solid lubricant 162 decreases over time, the pressing force of the solid lubricant 162 can be suppressed from decreasing. Therefore, the change of the amount of the powdery lubricant that is supplied to the lubricant supply target from the initial stage to the last stage can be minimized.
The reason why the above result is obtained is as follows.
In general, when the entire length of a spring of which the extension change amount changes from the initial stage to a stage where the solid lubricant 162 is completely consumed increases, the change of the biasing force of the spring with respect to the extension change amount of the spring decreases. In the pressing mechanism 563 shown in FIG. 16, a spring 563C needs to be disposed in a compressed state and a direction of the biasing force (pushing force) and the pressing direction of the solid lubricant 162 against the brush roller 161 need to be matched with each other. In this configuration, when the entire length of the spring increases, it becomes difficult to match the direction of the biasing force of the spring 563C and the pressing direction of the solid lubricant 162 against the brush roller 161. Therefore, there is a limitation in increasing the entire length of the spring. In the pressing mechanism 563 shown in FIG. 16, an arrangement space that corresponds to the length of the spring needs to be secured in a radial direction of the brush roller 161, which results in increasing a size of a device. For this reason, in the pressing mechanism shown in FIG. 16, a relatively short spring needs to be used. As a result, the change of the biasing force of the spring 563C with respect to the extension change amount of the spring 563C changing from the initial stage to the stage where the solid lubricant 162 is completely consumed is large. When the height of the solid lubricant 162 decreases over time, the pressing force of the solid lubricant 162 continuously decreases.
Meanwhile, in the pressing mechanism 463 that is described in Japanese Patent Application Laid-open No. 2007-293240, as shown in FIG. 15, the spring 163C can be disposed in an extended state and the solid lubricant 162 can be pressed against the brush roller 161 with the biasing force (tensile force). Therefore, even though the entire length of the spring is increased, the problem of the pressing mechanism that uses the compression spring shown in FIG. 16 is not generated. In the pressing mechanism 463 that is described in Japanese Patent Application Laid-open No. 2007-293240, a longitudinal direction of the spring 163C is matched with a longitudinal direction of the solid lubricant 162. Therefore, the length of the spring 163C can be increased by effectively using a space of the longitudinal direction of the solid lubricant 162. Even though the length of the spring 163C is increased, the arrangement space is not increased in the radial direction of the brush roller and the size of the device is not increased. For this reason, according to the pressing mechanism 463 that is described in Japanese Patent Application Laid-open No. 2007-293240, the spring 163C that is much longer than the compression spring 563C used in the pressing mechanism shown in FIG. 16 can be adopted. As a result, the change of the biasing force of the spring 563C with respect to the extension change amount of the spring 563C changing from the initial stage to the stage where the solid lubricant 162 is completely consumed is small. Even though the height of the solid lubricant 162 decreases over time, the pressing force of the solid lubricant 162 can be suppressed from decreasing.
FIG. 17 shows the force that acts on the movable member 463A of the pressing mechanism 463, on the basis of the technology described in Japanese Patent Application Laid-open No. 2007-293240.
In the pressing mechanism 463, the movable member 463A is configured to freely rotate using the attachment position 163B as the fulcrum. In this case, a point where the movable member 463A makes contact with the fixing wall (contacting portion) 164 is regarded as an action point, the length from the action point to the fulcrum is denoted by the symbol L, and an angle that is formed between a direction connecting the fulcrum and the action point and a pressing direction (vertical direction in the drawing) is expressed by ((Π/2)−θ). Further, a point where the movable member 463A receives the biasing force F from the spring 163C is regarded as a force point, the length from the force point to the fulcrum is denoted by the symbol I, and an angle that is formed between a direction connecting the fulcrum and the force point and a direction of the biasing force F is denoted by φ. At this time, according to the technology that is described in Japanese Patent Application Laid-open No. 2007-293240, the magnitude N of the force (force of a pressing direction of the fixing wall (contacting portion) 164 by the movable member 463A) that is generated at the action point is expressed by the following Equation (1).N=(I/L)×F×sin φ×cos θ  (1)
In this case, in the pressing mechanism 463 that is described in Japanese Patent Application Laid-open No. 2007-293240, if the solid lubricant 162 is decreased by being rubbed against the brush roller 161, the position of the force point shifts to the right side in the drawing, and the spring 63C is contracted. For this reason, the biasing force F by the spring 163C decreases. As a result, if the solid lubricant 162 is decreased by being rubbed, the biasing force F shifts in a direction where the magnitude of the force generated at the action point, that is, the pressing force N decreases. However, the decrease amount of the biasing force F with respect to the decrease amount of the solid lubricant 162 (increase amount of h) decreases, as compared with the pressing mechanism 563 shown in FIG. 16. Therefore, the decrease amount of the pressing force N with respect to the decrease amount of the solid lubricant 162 (increase amount of h) can be minimized.
If the solid lubricant 162 is decreased by being rubbed against the brush roller 161, the distance h in the drawing increases correspondingly to the decrease amount. As a result, the angle ((Π/2)−θ) that is formed between the direction connecting the action point and the fulcrum and the pressing direction (vertical direction in the drawing) decreases. That is, the angle θ increases. Therefore, according to the Equation (1) that is described in Japanese Patent Application Laid-open No. 2007-293240, when the solid lubricant 162 decreases, cos θ decreases and the magnitude N of the force that is generated at the action point decreases correspondingly to the decrease amount. However, in the pressing mechanism 463 that is described in Japanese Patent Application Laid-open No. 2007-293240, if the solid lubricant 162 decreases, the angle φ that is formed between the direction connecting the force point and the fulcrum and the direction of the biasing force F increases. Therefore, when the solid lubricant 162 decreases, sin φ increases. Since the magnitude N of the force generated at the action point increases correspondingly to the increase amount, according to the technology described in correspondingly to Japanese Patent Application Laid-open No. 2007-293240, at least a part of the decrease amount of N due to the decrease of cos θ can be offset by the increase amount of N due to the increase of sin φ.
In the pressing mechanism 463 that is described in Japanese Patent Application Laid-open No. 2007-293240, as shown in FIG. 15, the contact portion of the movable member 463A that contacts the fixing wall 164 has a circular arc shape. Thereby, a contact place of the movable member 463A with respect to the fixing wall 164 gradually changes according to the decrease of the solid lubricant 162. As a result, if the solid lubricant 162 decreases, the length L from the action point to the fulcrum increases. In this case, if the length L from the action point to the fulcrum increases, the magnitude of the force generated at the action point, that is, the pressing force N decreases. If the length L from the action point to the fulcrum increases, θ decreases. Therefore, a decrease rate of cos θ that decreases according to the decrease of the solid lubricant 162 can be minimized.
As such, according to the pressing mechanism 463 that is described in Japanese Patent Application Laid-open No. 2007-293240, if the solid lubricant 162 is decreased by being rubbed against the brush roller 161 and thereby h increases, based on this, L increases, F decreases, sin φ increases, and cos θ decreases. Meanwhile, as described above, as compared with the pressing mechanism 563 shown in FIG. 16, the decrease rate of F can be suppressed. By adopting the configuration where the length L from the action point to the fulcrum gradually increases, the decrease rate of cos θ can be suppressed. As a result, as compared with the pressing mechanism shown in FIG. 17, the decrease rate of the pressing force N can be suppressed. Therefore, even though the solid lubricant 162 is decreased by being rubbed against the brush roller 161, the change amount of the magnitude N of the force that is generated at the action point can be decreased. As a result, the change of the amount of the powdery lubricant that is applied to the lubricant supply target from the initial stage to the last stage can be minimized.
According to the pressing mechanism 463 that is described in Japanese Patent Application Laid-open No. 2007-293240, by increasing the length according to the decrease of the solid lubricant 162 and appropriately adjusting the various parameters to change the pressing force N, the change amount of the pressing force N from the initial stage to the last stage can be decreased, as compared with the pressing mechanism 563 shown in FIG. 16. However, in the pressing mechanism that is described in Japanese Patent Application Laid-open No. 2007-293240, in the last stage where the solid lubricant 162 of the predetermined amount or more is scraped off and the remaining solid lubricant 162 becomes small, the amount of the powdery lubricant that is supplied to the lubricant supply target is insufficient.
According to the pressing mechanism 463 that is described in Japanese Patent Application Laid-open No. 2007-293240, for example, when a solid lubricant formed through the melting process is used, by appropriately adjusting the various parameters, the powdery lubricant of the appropriate amount can be supplied to the lubricant supply target from the initial stage where the solid lubricant starts being scraped off to the intermediate stage. However, in the pressing mechanism that is described in Japanese Patent Application Laid-open No. 2007-293240, for example, when the solid lubricant obtained by compressing the powdery lubricant is used, the amount of the powdery lubricant that is supplied to the lubricant supply target in the initial stage becomes excessive.
As a result of zealous study, the inventor(s) found out that the problem of insufficient amount of the powdery lubricant supplied to the lubricant supply target in the last stage is caused by the following reason. That is, by recent extension of the life span of the solid lubricant 162, in the last stage, the capability of the supply member to scrape off the solid lubricant is lowered than the required capability over time. As a result, with the same pressing force as that in the initial stage or the intermediate stage, the sufficient amount of the powdery lubricant cannot be scraped off the solid lubricant in the last stage. For this reason, the amount of the powdery lubricant that is supplied to the lubricant supply target in the last stage is insufficient.
Therefore, in the invention according to a first aspect, the pressing force of the solid lubricant in the last stage becomes greater than the pressing force in the intermediate stage. As such, by increasing the pressing force of the solid lubricant in the last stage, the scraping capability of the supply member that is lowered in the last stage can be reinforced, and the scraped lubricant amount that is similar to or equal to the scraped lubricant amount in the intermediate stage can be realized in the last stage.
As a result of zealous study, the inventor(s) found out that the problem of excessive supply amount of lubricant in the initial stage in the case of using the solid lubricant obtained by compressing the powdery lubricant is caused by the following reason. That is, when the solid lubricant obtained by compressing the powdery lubricant starts to be scraped off by the supply member, the powdery lubricant may be formed into minute agglomerates due to rubbing and be peeled off from the solid lubricant. Thereby, the lubricant may be scraped off more than the desired scraping amount. As a result, the excessive supply amount of the lubricant in the initial stage is generated. Further, the peeling-off phenomenon of the powdery lubricant being formed into minute agglomerates and peeled off from the solid lubricant is rarely occurred in the intermediate stage. Therefore, the desired scraping amount can be stably obtained in the intermediate stage.
Therefore, in the invention according to a second aspect, the pressing force of the solid lubricant in the initial stage becomes smaller than the pressing force in the intermediate stage. As such, by decreasing the pressing force of the solid lubricant in the initial stage, the peeling-off phenomenon that is occurred in the initial stage can be suppressed and the scraped lubricant amount that is similar to or equal to the scraped lubricant amount in the intermediate stage can be realized in the initial stage.